Subject: Re: [16NG] [nwg-chair] NWG feedback on 16ng's IPv4 CS draft

From: "Riegel, Maximilian (NSN - DE/Munich)" <[email-masked]>
Date: Thu, 12 Feb 2009 11:39:44 +0100

Gabriel,
 
The WiMAX Forum NWG reviewed section 4-3 and Appendix C of
draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-04.txt and would like to make
a couple of remarks on the MTU issue:
 
- The I-D is not very clear about the MTU issues appearing in an IPv4
over IEEE 802.16 transmission system. The ambiguities mainly result out
of the vague definition of the IEEE 802.16 link comprising both the
radio part of the link as well as the part of the link between BS and
AR, when the functions are located in different entities.
 
- Section 4.3 in particular misses the discussion of the dependencies
between MTU size and the tunneling protocol deployed between BS and AR.
 
- Section 4.3 also misses, that there is no packet loss when the MTU
size limitation is caused by the encapsulation overhead on the link
between BS and AR. E.g. when GRE is used for the tunnel between BS and
AR, the transport IP layer can fragment the GRE packets to fit the
transport MTU on the link between BS and AR. Reassembly in the tunnel
endpoint at the AR will re-establish the original user IP packet.
 
- Please note that the reason of the WiMAX NWG to limit the MTU going
over IPv4-CS to 1400 Bytes was to avoid fragmentation on the link
between BS and ASN-GW as well as on the link between ASN-GW and CSN (MIP
tunnel). Fragmentation and re-assembly require considerable processing
power in the network elements.
 
- Appendix C makes statements which would require more detailed review
of the I-D by WiMAX NWG. In particular 'The addressing and operation of
IPv4-CS described in this document are applicable to the WiMAX networks
as well' has not been verified yet.
Furthermore 'Thus, WiMAX MS nodes should use this default (1400) MTU
value per the current specification [WMF].  However, due to reasons
specified in section 4.3 above, it is strongly recommended that future
WiMAX MS nodes support a default MTU of 1500 bytes, and that they
implement MTU negotiation capabilities as mentioned in this document.'
makes recommendations to WiMAX without understanding the real reasons
for the limitation of the MTU size in Mobile WiMAX.
 
We would recommend to 16ng to revise the sections on MTU size to better
explain the underlying issues leading to restrictions in the MTU size.
In particular the influence of tunneling inside the network should be
carefully discussed.
In addition we would kindly ask to either remove whole Appendix C on the
WiMAX MTU size or revise the text explaining the real issues in the
WiMAX architecture. In particular the statements on the applicability of
the I-D on the WiMAX architecture and the recommendation on future
modifications in the WiMAX architecture seem not to be very appropriate
to us.

Bye
Max
Vize Chair NWG

________________________________

From: ext Gabriel Montenegro [mailto:[email-masked]] 
Sent: Monday, November 03, 2008 11:59 AM
To: [email-masked]
Cc: 'Daniel Soohong Park'
Subject: [nwg-chair] NWG feedback on 16ng's IPv4 CS draft

Prakash, Max and Yong Chang,

The IETF 16ng WG has published a revision of this draft:

"Transmission of IPv4 packets over IEEE 802.16's IP Convergence
Sublayer"

Per this announcement:

http://www.ietf.org/mail-archive/web/16ng/current/msg00863.html
<http://www.ietf.org/mail-archive/web/16ng/current/msg00863.html> 

We understand that this specification currently is not normative to NWG
(as opposed to RFC5121 on IPv6 CS). Nevertheless, given its relevance,
and with the hope it may become normative to NWG in some future
revision, the 16ng WG would like to solicit feedback from NWG on this
draft. 

In particular, please note that this draft specifies a default MTU of
1500,  which is different from the WiMAX-specified MTU of 1400 (per the
recently approved R1_V1.3.0-Stage-3  NWG specifications).  For MTU
discussion, please refer to these sections:

http://tools.ietf.org/html/draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-04#
section-4.3
<http://tools.ietf.org/html/draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-04
#section-4.3> 
http://tools.ietf.org/html/draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-04#
appendix-C
<http://tools.ietf.org/html/draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-04
#appendix-C> 

The 16ng WG will next meet on Nov 18 during the IETF in Minneapolis
(https://datatracker.ietf.org/meeting/73/agenda.html). If at all
possible, it would be best if comments were received before that date in
order for the WG to discuss them during the meeting.

Please send your comments to the [email-masked] <mailto:[email-masked]>
mailing list.

Thanks,

Gabriel and Daniel
16ng co-chairs